The equilibrium between unassociated (ribosome-free) cytoplasmic messenger ribonucleoprotein (mRNP) and polysome-associated mRNP is likely to be a key step in the translational control of cell proliferation. Therefore, the relative amounts and kinetics of these classes of mRNP and their nuclear precursors (hnRNP) will be studied in an organ (the kidney) that can be made to show graded responses from hypertrophy to hyperplasia to neoplasia. Renal hypertrophy will be produced by contralateral nephrectomy, hyperplasia by injection of folic acid, and neoplasia by dimethylnitrosamine treatment of Charles River mice. Particular attention will be paid to homologies in the protein components of the RNPs as assessed by labeling and by two-dimensional gel electrophoresis and the kinetics of labeling the integral RNA which may indicate precursor-product relationships. These proteins may stabilize the RNPs during stimulated growth and modulate the processing and translation of their RNAs; other work in this laboratory strongly suggests that the rate of degradation of protein and ribosomal RNA, rather than the rate of synthesis, is a major controlling mechanism in renal growth. The relative efficiencies of isolated RNP complexes in total protein synthesis will be measured in a cell-free protein synthesizing system and compared to that of deproteinized poly(A)-containing mRNA and reconstituted RNP systems. We propose to show that RNP complexes isolated during different patterns of growth contain some differences in their protein complements, that these differences are directly related to the control of mRNA expression and that these proteins determine the distribution of mRNA between translating and non-translating states.